1. Field of the Invention
This invention relates generally to temperature measurement and, more particularly, the invention relates to infrared clinical thermometers.
2. Description of the Related Art
Conventional ear thermometers employ an infrared (IR) detector for sensing the temperature inside the ear at the tympanic membrane. The infrared detector is mounted within a heat sink so as to stabilize an ambient reference temperature. As conventionally mounted, the detector is too large to be inserted into the ear canal leading to the tympanic membrane. Accordingly, a waveguide, typically formed of a polished tube, is interposed between the tympanic membrane and the IR detector. The use of a waveguide involves a number of drawbacks resulting, for example, from its non-zero emissivity, its relatively high cost, and the complexity of the resultant structure.
One embodiment of the invention is an infrared ear thermometer. The infrared ear thermometer-includes a detector head housing having a heat sink with a recess. A thermopile sensor is mounted in the recess. The recess defines an aperture that limits the field of view of the thermopile sensor. The thermometer also includes a thermal sensor and temperature determination circuitry configured to calculate a temperature in response to output of the thermopile sensor and the thermal sensor.
Another embodiment of the infrared ear thermometer includes a detector head housing having a heat sink with a recess. A thermopile sensor is mounted in the recess. The thermopile sensor has a hot junction and a cold junction, the hot junction being responsive to infrared radiation. An output signal of the thermopile sensor is related to a temperature difference between the hot junction and the cold junction. A thermal capacity of the hot junction, a thermal conductivity between the hot junction and the cold junction, a thermal capacity of the cold junction, a thermal conductivity between the cold junction and the heat sink, and a thermal capacity of the heat sink are selected so that the output signal of the thermopile sensor stabilizes or has a flat peak during a temperature measurement. A thermistor is mounted in thermal communication with the cold junction. Temperature determination circuitry calculates an output temperature in response to the output signal of the thermopile sensor and an output of the thermistor.
Another embodiment of the infrared ear thermometer includes a detector head housing having a heat sink with a recess. A thermopile sensor is mounted in the recess. The thermopile sensor has a hot junction and a cold junction, the hot junction being responsive to infrared radiation. The output signal of the thermopile sensor is related to the temperature difference between the hot junction and the cold junction. A thermistor is mounted in thermal communication with the cold junction. A heat pipe, made of a thermally conductive material, surrounds a portion of the thermopile sensor, whereby the heat pipe prevents heat transfer from an ear canal to the hot junction. Temperature determination circuitry calculates an output temperature in response to the output signal of the thermopile sensor and an output of the thermistor.
Another embodiment of the invention is a method for determining the temperature of a subject. Successive temperature measurements of the subject are taken using an infrared thermometer. A plurality of most recent measurements are stored in a moving time window. An average of up to all of the plurality of stored measurements is successively calculated. The difference between successive averages is calculated and a determination is made whether the difference is less than a predetermined value. Finally, a calculated temperature is output.
Another embodiment of the invention is a method for calculating a subject""s temperature based upon output values from a thermopile and a thermistor of an infrared thermometer, wherein the thermistor is in thermal communication with a cold junction of the thermopile, and wherein the hot junction is in infrared communication with an object to be measured. The temperature of the cold junction is determined with the thermistor. A bias and a slope of the thermopile are looked up in a lookup table based upon the temperature of the cold junction. The output signal of the thermopile is measured. Finally, a temperature is calculated based upon a linear relationship defining temperature as a function of the output signal of the thermopile in terms of the bias and the slope.
Another embodiment of the invention is an infrared thermometer for measuring temperature of a subject""s forehead. The infrared ear thermometer includes a detector head having a metal heat sink. A thermopile sensor is mounted to the front of the heat sink with a thermopile sensor mounted in the recess. A thermistor is mounted in thermal communication with a cold junction of the thermopile sensor. The outer surface of the detector head includes an extension for placement against the subject""s forehead, wherein the extension forms an air pocket isolating a portion of the forehead from air flow outside the air pocket.
Another embodiment of the infrared thermometer for measuring temperature of a subject""s forehead includes a detector head having a metal heat sink. A thermopile sensor is mounted to the front of the heat sink with a thermopile sensor mounted in the recess. A first temperature sensor measures a cold junction temperature of the thermopile sensor. A second temperature sensor provides fast measurement of a room ambient temperature. An electronic circuit calculates the temperature of the subject based in part upon the input of the second temperature sensor.
Another embodiment of the invention is a detector head housing for an infrared clinical thermometer. The housing includes a body made of a soft plastic material. The body has an outer surface configured to make contact with a subject. A liquid having a high thermal capacity fills a portion of a cavity formed within the body. The high thermal capacity liquid thermally isolates an infrared sensor within the body from heat generated by the subject.
Another embodiment of the infrared ear thermometer includes a detector head housing having a heat sink with a recess. A thermopile sensor is mounted in the recess. A sleeve that defines an aperture that limits the field of view of the thermopile sensor fits into the recess. The thermometer also includes a thermal sensor and temperature determination circuitry configured to calculate a temperature in response to output of the thermopile sensor and the thermal sensor.